1. Field of the Invention
The present invention relates to a semiconductor device, in particular, a semiconductor device including a fuse element that can be cut for changing a circuit configuration of the semiconductor device.
2. Description of the Related Art
There is a method of changing a circuit configuration of a semiconductor device by cutting, in a semiconductor device manufacturing process, a fuse element formed of polysilicon, metal, and the like by using, for example, a laser after a wafer manufacturing process is finished. By using this method, a resistance value can be corrected to obtain desired characteristics after electrical characteristics of the semiconductor device are measured. This method is thus effective particularly for a semiconductor device that places emphasis on its analog characteristics.
In this method, it is required for the fuse element to be stably cut by the laser and have a high corrosion resistance. Hitherto, an insulating protective film is formed on an upper portion of a semiconductor device, and, for example, a silicon nitride film is used for the purpose of preventing the penetration of moisture from the outside and other purposes. However, because a fuse element is supposed to be cut by laser irradiation later, the silicon nitride film that absorbs the laser cannot be arranged on the fuse element, and hence the protective film formed above the fuse element is removed so as to open the protective film. Therefore, the fuse element is easily affected by the penetration of moisture and needs to have an improved corrosion resistance.
In Japanese Patent Application Laid-open No. 2011-49252, there is proposed a method of improving a corrosion resistance by forming a moisture resistance insulating film such as a silicon nitride film or a silicon oxynitride film on at least a side surface of a fuse element, or on the side surface and an upper portion of the fuse element in such a manner that the moisture resistance insulating film is thinner on the upper portion than on the side surface.
However, the above-mentioned related art has the following problems. Although moisture basically penetrates from a portion above the fuse element from which the protective film is removed, in the method, no moisture resistance insulating film is arranged or the thin moisture resistance insulating film is formed on the upper portion of the fuse element. Therefore, the protection of the upper portion is insufficient. Further, because the silicon nitride film or the silicon oxynitride film is used as the moisture resistance insulating film, the radiated laser beam is absorbed, which makes it difficult to cut the fuse. In this method, the moisture resistance improvement and the stability of cutting the fuse element by the laser have a trade-off relationship. It is considered that obtaining a condition that satisfies both requirements is difficult to achieve. In particular, the related-art configuration focuses only on an uncut fuse element and has no effect on a fuse element cut by the laser. This is because, when the fuse element is cut, the fuse element is exposed from the cut surface to cause corrosion. The fuse element is corroded from the cut surface and the fuse element thus expands, resulting in cracking of the insulating film formed on the fuse element. Further, a problem arises in that the crack becomes a penetration route of the moisture, and hence the corrosion progresses inside the semiconductor device.